T HE Straub phenomenon is a well known reaction in pharmacology, first described by Otto Hermann, a pupil of the famous pharmacologist, Walter Straub. It was first published under the title of Eine Biologische Nachweismethode des Morphins (1912, Biochemische Zeitschrift, 39: 216). The author describes a characteristic stiffening and erection of the tail in mice after injection of morphine. This upbending in extreme cases assumes an S shape, but such an S shape does not usually occur and any degree of stiffness and bending back of the tail is considered a positive Straub reaction. This phenomenon is exhibited also by white rats but because of the heavy tail in those animals the bending usually consists of a so-called poker tail. The Straub phenomenon was originally thought to be diagnostic for morphine but was found even by Straub and his pupils to be produced by other morphine derivatives and also by some of the other alkaloids, particularly by nicotine. Later work by Professor Van Leersum, Dutch professor in Leiden, showed that the Straub phenomenon is due to a spasm of the sphincter ani produced by the action of drugs or poisons either directly on the muscle of the sphincter or indirectly through an action on the spinal column (1918, Nederlandsch Tijdschrift voor Geneeskunde, 62: 1374). This interesting phenomenon, even in the original communication, was described as not possessing any quantitative exactness and, therefore, could not be relied upon from a forensic point of view as sufficient evidence for the presence of morphine in the body tissues or fluids, but it does serve as a lead to be followed and corroborated by exact chemical work. Macht showed that the phenomenon produced by morphine and its derivatives is really due to one part of the morphine molecule (1920, Proc. Soc. Exp. Biology and Medicine, 17: 100), namely the piperidine nucleus, so that the chemical piperidine alone can also produce it. As a matter of fact, this spasm of the sphincter ani and consequent raising of the tail is obtained in mice even after intraperitoneal injections of various irritating solutions and of distilled water alone which is also irritating to the peritoneum. More recently the mouse tail test has been advocated as a means of detecting doping in race horses, because when morphine is administered to a horse it is excreted in the saliva. While this is true, such a test is not at all conclusive because all kinds of drugs or chemicals found in the saliva may give a mouse tail reaction. Thus, for instance, the present writer found that potassium sulphocyanate, a normal constituent of saliva, when injected in mice and white rats may produce a Straub phenomenon. Again a chemical known as D.O.T.G. or di-ortho-tolyl guanidine, used as a vulcanizer in the manufacture of rubber washers, etc., can also produce not only a positive Straub mouse-tail reaction, but give some of the chemical color reactions of morphine. Thus, saliva kept in a jar with such a rubber washer may give a misleading Straub phenomenon.